Which layer of the atmosphere protects humans from radiation?

The Stratosphere is the correct layer of the atmosphere responsible for protecting humans from harmful radiation, particularly ultraviolet (UV) rays from the sun. This layer contains the ozone layer, which plays a critical role in absorbing the majority of the sun's harmful UV radiation. Without this protective shield, increased levels of UV radiation would reach the Earth's surface, leading to higher rates of skin cancer, cataracts, and other health issues, as well as negative impacts on ecosystems.

The other layers of the atmosphere, while important, do not fulfill this specific protective function. The Troposphere is primarily where weather occurs and contains the majority of atmospheric mass, but it lacks the ozone that characterizes the Stratosphere. The Mesosphere extends above the Stratosphere and has a very low density of molecular gas, offering little to no protection against radiation. The Thermosphere is much higher up and can absorb high-energy radiation; however, it does not contain the ozone layer that is essential for blocking UV rays effectively at lower altitudes where humans and most living organisms exist.